1. Field of the Invention
The present invention relates to a communication apparatus in an Ethernet passive optical network (EPON), and more particularly, to an EPON bridge sublayer for supporting point-to-point communications between optical network units (ONUs) in the EPON.
2. Description of the Related Art
An EPON is a passive optical subscriber network technology that is designed to apply Ethernet used in the existing local area network (LAN) to a general subscriber network. The EPON is a point-to-multipoint network that is formed of a PON that a number of ONUs located at the subscriber side are passively connected to an optical line termination (OLT) at the network side through a passive splitter.
The EPON is a shared media topology with a tree-like structure. Unlike media sharing in the existing Ethernet, due to characteristics of an optical path and the passive splitter, a downstream frame from the OLT to an ONU is transmitted to all ONUs. An upstream frame transmitted from an ONU has a transmission direction, such that it cannot be received by any other ONU, but can be only received by the OLT. Also, an Ethernet frame is used to perform communications between the OLT and the plurality of ONUs.
As a subscriber network solution, IEEE 802.3ah Ethernet in the First Mile (EFM) Task Force has been working toward standardization for the EPON.
Ethernet employing carrier sense multiple access/collision detect (CSMA/CD) allows a terminal connected to shared media and point-to-point links to directly communicate with another terminal. In “native mode” PON, broadcasting is performed in a downstream direction and point-to-point transmissions between an OLT and ONUs are performed based on time division multiple access (TDMA) in an upstream direction. However, when an IEEE 802.1D spanning tree is used in the PON, a loop is inadvertently generated.
In the PON, in order for an ONU to transmit a frame to another, an OLT has to look at a destination address of the frame and relay the frame to a destination ONU. However, according to the existing Ethernet standards, the OLT cannot return a received frame to an ONU and an ONU occurs the problem that a media access control (MAC) frame is input to an ONU again through a port which the ONU outputs the MAC frame.